The invention relates to an optical fiber sensor, notably a strain sensor using optical fibers and their property of intrinsic birefringence. More particularly, it relates to a mechanical strain sensor and a thermal detector. A birefringent optical fiber may be used in two main ways:
to maintain or preserve a given state of polarization (the propagation of the wave along a characteristic axis);
as a polarimeter (differential propagation along both axes of polarization).
The system of the invention applies to these modes of use.